1. Field
This patent specification relates to an optical writing system provided with at least two laser diodes capable of properly correcting hue deviations. Also, image forming apparatuses incorporating the optical writing system, inclusive of color laser printers, full color digital duplication apparatuses, and digital multiplex machines. Also, a method of correcting the hues implemented through computation processing.
2. Discussion of the Background
Techniques related to the correction of output images for optical writing system have been disclosed in Japanese Laid-Open Patent Application No. 10-226104, in which a printer capable of processing images with high quality at high speed is formed by using video clock signals delayed by a delay circuit having the phase matched to a horizontal start signal.
In the printer, there are provided a plurality of delay elements for delaying an original video clock signal and a selection circuit for selecting video signals having a phase in agreement with the horizontal start signal out of the delayed signals.
In general, an image forming apparatus such as, for example, a digital color image forming machine consists of several units in addition to photoreceptor belt, including a pre-exposure unit (discharging unit), primary charging unit equipped with a grid, light exposure unit for imaging equipped with an LD as a light source, surface electrometer for measuring surface potential of the photoreceptor belt, developing unit, transfer charger, separation charger, cleaning, etc.
On the other hand, the aforementioned application No. 10-226104 discloses, since video clock signals delayed by the delay circuit having the phase matched to a horizontal start signal are selected out of original video clock signals in a video clock synchronization circuit or video clock signals delayed by the delay circuit with the plurality of delay elements, it becomes feasible to generate video clock signals phase matched to a horizontal start signal and to handle high speed outputting of images.
Although the phase matching is feasible by the abovementioned techniques between video clock signals (which are hereinafter referred to as image clock signals) and horizontal synchronization signals, numerous similar methods are already present for controlling the phase of video clock signals.
Although image correction of the dot forming position for the terminating edge in the main scanning direction may be feasible to a certain extent by utilizing the difference in image magnification for respective LDs according to the noted techniques, problems exist regarding (1) eliminating the effects on images of the difference caused by a large power output difference between two LDs and beam pitch deviation and (2) acquiring stable image qualities.
Furthermore, when phase control is intended for image clock signals to be adjusted arbitrarily to compensate the frequency change caused in the LD by deterioration over time, the noted techniques provide inadequate control.
Accordingly, what needed is a method of precise phase control for image clock signals.
It is desirable that the method is capable of properly shifting the phase of image clock signals to compensate for the deterioration of LD over time and the variation of LD characteristics caused by frequency fluctuation, so that positional precision from a synchronization point for respective LDs is assured and picture images at the terminating edge in the main scanning direction can be stabilized.
It is further desirable that the method is capable of eliminating difficulties in generating proper hues from dot positioning precision which is common to full color image formation using two or more LD light sources.
Moreover, it is also desirable that the method attain both the stabilization of picture images at a terminating edge in a main scanning direction and the elimination of deficiencies in generating proper hues from dot positioning precision, simultaneously.
Further, it is desirable that control of image quality be controllable at user's own discretion on full color images which may be formed in a variety of qualities and resulting from a difference in wavelength, a power output of respective LDs, and in the beam pitch between the LDs, so that the user selection can properly be made regarding hue variations in half tone image portions formed with dither patterns, whereby excellent image qualities can maintained.